Probing the activated complex of the F + NH 3 reaction via a dipole-bound state.

Experimental characterization of the transition state poses a significant challenge due to its fleeting nature. Negative ion photodetachment offers a unique tool for probing transition states and their vicinity. However, this approach is usually limited to Franck-Condon regions. For example, high-lying Feshbach resonances with an excited HF stretching mode (v HF  = 2-4) were recently identified in the transition-state region of the F + NH 3  → HF + NH 2 reaction through photo-detaching FNH 3 - anions, but the direct photodetachment failed to observe the lower-lying v HF  = 0,1 resonances and bound states due apparently to negligible Franck-Condon factors. Indeed, these weak transitions can be resonantly enhanced via a dipole-bound state (DBS) formed between an electron and the polar FNH 3 species. In this study, we unveil a series of Feshbach resonances and bound states along the F + NH 3 reaction path via a DBS by combining high-resolution photoelectron spectroscopy with high-level quantum dynamical computations. This study presents an approach for probing the activated complex in a reaction by negative ion photodetachment through a DBS.